MINOR SPOILERS AHEAD!
Not difficult at all. Only certain parts are difficult but only because they require you to think on how to strategically beat the enemies.
-For normal enemies use the revolver.
-For the huge enemies that are like 7 ft tall use high powered guns like the hunting rifle or shotguns.
-Learn how to use the dodge move (LB+LS), it saved my neck many, many times.
-When your health goes down and there are several enemies do not hesitate to throw down a flare, that will keep enemies away.
-For the poltergeist (movable objects) always try to get behind cover, even simple poles and even boxes will do the job as the poltergeist won't hit you.
-If the birds keep rushing you and you're not able to hit them with your flashlight, it's a good technique to hold up a flare in your hand.
-If you are low on health and low on ammo and items, look for the nearest source of light. Throw down a flare and make haste towards the nearest light.
I'd recommend you do this on your first play through as it's not that hard. I even managed to accumulate 73 manuscripts and 73 thermos during my first playthrough in hard difficulty.